The present invention relates to a lengthwise folding arrangement, particularly for webs which are taken from a roller rotary printing machine and supplied to a rotary folder, a transverse cutter and the like.
Lengthwise folding arrangement in which more or less small partial strip changes its path are also known as plow folding arrangements in strands folding arrangement. Such an arrangement is disclosed, for example, in the U.S. Pat. No. 3,799,536. In this arrangement a laterally adjustable and substantially horizontal guiding plate is mounted on two blocks so that it extends only in accordance with the predetermined turning or folding width in the plane of the paper web. The web is guided from a drawing-in roller which is arranged higher, over a front side of the laterally adjustable guiding plate provided with a curvature, and is folded with the aid of a rounded corner provided on the plate curvature in a plow-like manner over the longitudinal edge of the guiding plate. The part of the web which is not guided under the guiding plate is first partially and then fully turned and pressed on the upper side of the plate by an adjustable tubular guiding roller. The not folded part of the web is guided under the plate curvature toward the lower side of the guiding plate. The web is then withdrawn either by the driven withdrawing roller or by the subsequent aggregates.
This construction possesses the disadvantage that the geometrical form of the plow-corner of the plate curvature is always fixed and cannot be adjusted in its shape to the different thicknesses or types of the paper to be treated. Moreover, the pressing by the paper guiding roller which operates shortly behind the plow-like corner leads to the fact that the turned part of the web is folded over a very short path which leads to a forced running connected with high pulling stresses and thereby to overextension of the web in the folding region. The extremely differing web expansion of the folded part of the web and the part of the web guided onto the adjustable plate obtains for many types of paper folds and other problems with which the further treatment of the entire web is performed not simultaneously as desired or after the folding separation by cutting of the part of the web takes place. For production of folded or partially folded advertising printing matter, etc. these arrangements are not suitable. Also, the required accuracy of the folding line is not achieved, since the very short-distance turn of the part of the web can lead to buckling of the web.
The U.S. Pat. No. 4,052,048 shows an arrangement for lengthwise folding of the webs, which is provided with an adjustable guiding rod extending substantially diagonally over the folding plate and used for example for zig-zag folding of fabric webs and other webs which are to be treated so as to form towels, napkins and the like. The U.S. Pat. No. 4,047,711 discloses a plow-folding arrangement with a folding device which is easily adjustable and displaceable during running of the web. However, it has the disadvantage of the unchangeable geometrical form of the corner of the plate curve, on the one hand, and its manufacture and maintenance is very complicated and expensive on the other hand.